Search This Blog

Importance of Water Quality in Aquaculture

Fish perform all their bodily functions in water. Because fish are totally dependent upon water to breathe, feed and grow, excrete wastes, maintain a salt balance, and reproduce, understanding the physical and chemical qualities of water is critical to successful aquaculture. To a great extent water determines the success or failure of an aquaculture operation.

Physical Characteristics of Water

Water can hold large amounts of heat with a relatively small change in temperature. This heat capacity has far reaching implications. It permits a body of water to act as a buffer against wide fluctuations in temperature. The larger the body of water, the slower the rate of temperature change. Furthermore, aquatic organisms take on the temperature of their environment and cannot tolerate rapid changes in temperature. Water has very unique density qualities. Most liquids become denser as they become cooler. Water, however, gets denser as it cools until it reaches a temperature of approximately 39ºF. As it cools below this point, it becomes lighter until it freezes (32ºF). As ice develops,water increases in volume by 11 percent. The increase in volume allows ice to float rather than sink, a characteristic that prevents ponds from freezing solid. Far from being a "universal solvent," as it is sometimes called, water can dissolve more substances than any other liquid. Over 50 percent of the known chemical elements have been found in natural waters, and it is probable that traces of most others can be found in lakes, streams, estuaries, or oceans.

Water Balance in Fish

The elimination of most nitrogen waste products in land animals is performed through the kidneys. In contrast, fish rely heavily on their gills for this function, excreting primarily ammonia. A fish's gills are permeable to water and salts. In the ocean the salinity of water is more concentrated than that of the fish's body fluids. In this environment water is drawn out, but salts tend to diffuse inward. Hence, marine fishes drink large amounts of sea water and excrete small amounts of highly salt-concentrated urine (Figure 1). In fresh-water fish, water regulation is the reverse of marine species. Salt is constantly being lost through the gills, and large amounts of water enter through the fish's skin and gills (Figure 2). This is because the salt concentration in a fish (approximately 0.5 percent) is higher than the salt concentration of the water in which it lives. Because the fish's body is contantly struggling to prevent the “diffusion” of water into its body, large amounts of water are excreted by the kidneys. As a result, the salt concentration of the urine is very low. By understanding the need to maintain a water balance in freshwater fish, one can understand why using salt during transport is beneficial to fish.

Figure 1. Direction of water, ammonia, and salt movements into and out of saltwater fish. Saltwater fish drink large amounts of water and excrete small amounts of concentrated urine.

Figure 2. Direction of water, ammonia, and salt movement into and out of freshwater fish. Freshwater fish do not drink water, but excrete large amounts of dilute urine.

Water Quantity

The beginning aquaculturist usually underestimates the quantity of water required for commercial production. It is generally accepted that a minimum rate of 13 gallons per minute (gpm) is required for each surface acre of ponds. With this in mind, a 100- acre fish farm will need to have wells capable of producing 1,300 gpm of water. Such large volumes are required to replace water lost to evaporation and seepage. In addition, the farmer may have several ponds to fill quickly during the spawning season. In raceway culture, it is advisable to have a minimum flow rate of 500 gpm. Even water recirculating systems that recycle water require large quantities of water. If a 100,000 gallon capacity water recirculating operation exchanges 10 percent of the water daily, it will require 10,000 gallons of water per day. The availability of subsurface groundwater in Indiana and Illinois varies widely, ranging from as little as 10 gpm or less to over 2,000 gpm from properly constructed, large diameter wells. With the exception of the aquifers located along major river drainages (usually high yields), potential yields are divided into three distinct regions:
Northern Indiana and Illinois are good to excellent and, exclusive of some areas near northwestern Indiana, yields from 200-2,000 gpm can be expected.
In the central portion of Indiana and Illinois, groundwater conditions range from fair to good.
Well yields from 100-400 gpm are typical for many large-diameter wells. Many areas of southern Indiana and Illinois lack ground-water; generally, less than 10 gpm are available from properly constructed wells. In these areas, the major sources of groundwater are present in the sand and gravel deposits of the river valley aquifers.
These yield potentials do not indicate that an unlimited number of wells can be developed in given location. Detailed studies, including exploratory drilling and test pumping, should be conducted to adequately evaluate the groundwater resource in any given area. The resultant change in the water table is produced by spheres of influence from nearby wells.

1 comment:

purvajaaa said...

Importance of Water Quality in Aquaculture
thanks for sharing
water treatment plants